Indi,
A husband who isn't emotionally attached to his wife doesn't mind if she sleeps with someone else, especially if he can get pleasure out of it as well. Not all guys will admit this, but you can bet that's it there. It comes down to how you feel about the whole thing. You've taken this situation and have done a good job in seeing your options, so full credit to you for that. What you want is important. I know that if i'm in a situation where it's for the wrong reasons and it isn't me, i have to change it.
-to be nobody but yourself in a world which is doing its best, night and day, to make you everybody else means to fight the hardest battle which any human being can fight; and never stop fighting.- e.e.cummings